The Principles of Clinical Cytogenetics - Extra Materials - Springer

Human Chromosome Nomenclature 31
Fig. 3. Examples of metacentric, submetacentric, and acrocentric chromosomes.
Table 2
Frequently Used Banding Methods and Their Abbreviations
Banding Method Abbreviation
Q-bands Q
Q-bands by quinacrine derivatives
and fluorescence microscopy
QFQ
G-bands G
G-bands by trypsin and Giemsa GTG
C-bands C
C-bands by barium hydroxide and Giemsa CBG
R-bands R
R-bands by acridine orange RFA
and fluorescence microscopy
R-bands by BrdU and Giemsa RBG
Telomere bands or T-bands T
(1971) introduced a numbering system helpful in designating specific bands and regions. New terminology
and abbreviations were introduced to help explain chromosome abnormalities in a more meaningful
way. Other conferences then followed, with the latest held in Memphis in 1994. Descriptions
of human chromosomes and their abnormalities utilize a series of symbols and abbreviations. A
partial list of recommended symbols and abbreviations in ISCN 2005 appear in Table 3.
The centromere “cen” divides a chromosome into a short or “p” arm (from the French petit) and a
long or “q” arm. For descriptive purposes, the centromere is composed of two portions. The portion
of the centromere lying between its middle and the first band on the short arm is designated as “p10.”
Similarly, the portion of the centromere lying between its middle and the first band on the long arm is
designated as “q10.” The designations p10 and q10 allow us to describe accurately the nature and
organization of centromeres in isochromosomes, whole-arm translocations, and Robertsonian translocations
(see below). Each arm ends in a terminus (“ter,” thus “pter” and “qter”), where telomeres
are present to prevent the chromosomes from having “sticky ends.”
Each chromosome arm is divided into regions. This division is based on certain landmarks present
on each chromosome. By definition, a landmark is “a consistent and distinct morphologic area of a
chromosome that aids in the identification of that chromosome.” A region is an area that lies between
two landmarks. The two regions immediately adjacent to the centromere are designated as “1” (p1
and q1), the next distal as “2,” and so on. Regions are divided into bands and the bands into subbands
(see Fig. 5). A band is that part of a chromosome that is distinctly different from the adjacent area by
virtue of being lighter or darker in staining intensity. Sequential numbering of chromosome arms and
bands helps make the designation of specific bands easy. For example, the terminal band on the long